Open the Photos app
Tap Library or Albums
Select the photo or photos you want to delete
Tap the Trash icon
Tap Delete Photo or Delete X Photos
Open the Recently Deleted album
Tap Select
Tap Delete All or choose the photos you want to remove
Tap Delete Photo or Delete X Photos
Go to Settings
Tap Photos
Turn off iCloud Photos if you do not want deleted photos to sync across devices
If using iCloud Photos, delete the photos from all synced devices before emptying Recently Deleted
Back up any photos you want to keep before deleting them
Check the Files app, Messages, Mail, and third-party apps for copies if needed